1. Field of the Invention
The present invention relates to a spray nozzle for liquid, in particular for coating liquid under high pressure. Furthermore, the invention relates to a device for spraying liquid, in particular for coating liquid under high pressure, comprising such a nozzle.
2. Brief Description of the Related Art
A device for spraying liquid or sprayer, either of the manual type or of the automatic type, generally comprises a spray nozzle, sometimes several, which is(are) mounted at the downstream end of the sprayer. The terms “upstream” and “downstream” herein refer to the direction of flow of the liquid in the sprayer. The term “upstream” denotes elements located on the side of the sprayer where the liquid to be sprayed arrives from a supply source. The term “downstream” denotes elements located on the side of the sprayer where the liquid is sprayed in droplets.
Such a sprayer may, for example, be intended for spraying coating liquids such as waterborne or solvent-based paints. To produce the spraying of the liquid in droplets, the sprayer is connected, by means of one of more tube(s), to a pump designed to put the liquid under high pressure, for example 70 bars. The spraying is carried out at the downstream end of the nozzle, which has a geometry determined depending on the desired shape for the jet of droplets of the sprayed liquid.
To the aim of shaping the jet of sprayed liquid into a “fan”, usually called a “flat” spray, a nozzle such as that illustrated by FIGS. 1 and 2 is known from the prior art. As FIG. 1 shows, the nozzle 1 comprises a body 2 which defines, on the upstream side, a chamber 3 through which the liquid arrives and, on the downstream side, a channel 4 for conveying the liquid from the chamber 3 through to the outlet of the nozzle 1. The chamber 3 and the channel 4 extend along a longitudinal axis X1-X′1 of the nozzle 1. Downstream of the channel 4, the nozzle 1 comprises a slot 6 intended to shape the liquid jet into a flat spray. As FIGS. 1 and 2 show, the slot 6 is formed by two surfaces 61 and 62 which are plane, which converge in the direction of the channel 4, and which are positioned on either side of a plane P6 including axis X1-X′1. The one-eyed bottom of the channel 4 obtained in the body 2 before milling the slot 6 has the form of a hollow dome 5, which is herein referred to by the word “dome”. The dome 5 connects the channel 4 and the slot 6.
In nozzles of the prior art, the dome 5 has the shape of an ogive or triangular arch or a hemispherical shape, the length of which approximately equals the diameter of the channel 4. As FIG. 2 shows, the intersection of the dome 5 with the surfaces 61 and 62 of the slot 6 defines an outlet orifice 7 of the nozzle 1 in the overall shape of a flattened ellipse.
When the nozzle 1 sprays a liquid under high pressure, for example 70 bars, the geometry of the orifice 7 shapes the jet into a cone with an elliptical cross section. With the nozzle 1, the flow rate of the sprayed liquid is not uniformly distributed in this elliptical cross section. On the contrary, it has higher concentrations towards the distant edges of the ellipse. In the field of spraying coating liquids, this type of distribution of liquid is called the “tails effect”. It has been observed that the more rounded the edges of the ellipse are, the larger are the “tails” in the flow of liquid.
The “tails effect” has the drawback of leading to asymmetric wear of the nozzle 1, by overwearing down the edges of the orifice 7. The more abrasive the sprayed liquid is, the greater this wear is. This wear increases the “tails effect” and therefore leads to a reduction in the quality of the spraying. In addition, it reduces the service life of the nozzle 1, even when the material of the body 2 has a high hardness.
GB-A-1 312 052 describes a flat spray nozzle comprising a discontinuity at the junction between the channel and the dome connecting the channel and the slot of the nozzle. However, the nozzle of GB-A-1 312 052 does not permit to significantly decrease the “tails effect” so as to get a sufficient spraying quality.